Eldon wrote ...
What is the relationship (if any) between C522, A523, 523-, and 524-?
..........

Essentially they are the same; and the changes should largely be ignored
as there is just too much variety to be meaningful.

But to explain things: If you look at the 514-525 part of the the mtDNA
in the Cambridge Reference Sequence (CRS) the bases are:
CACACACACACC
i.e. 5 pairs of repeating CA's followed by a single CC.

and there are many different ways to describe the mutations in this 'variable stretch'.

The commonest change seen throughout Haplogroup H is:
- the loss of a 'CA' pair; and to call this loss '522- 523-' , or 'd522-523'.
(or if you should prefer, 523- 524- - which to me is not so logical).

And another common change, seen in H1, is to gain a 6th. CA; and call it
'523+ 523+' or '523CA'.